[A Case of Breast Cancer with Bone Marrow Metastasis in a Patient with a History of Systemic Lupus Erythematosus and Autoimmune Hemolytic Anemia].

A 45-year-old female with a medical history of systemic lupus erythematosus presented with breast cancer. On postoperative day 26 after undergoing left mastectomy and axillary lymph node dissection, she reported fever and anorexia at the outpatient clinic. Laboratory findings showed pancytopenia, and a subsequent bone marrow biopsy confirmed metastatic breast cancer involving the bone marrow. Tamoxifen and goserelin therapy was started initially. However, on the day after treatment initiation, the patient experienced rapid progression of anemia, with laboratory evidence of hemolysis and clinical signs of jaundice and splenomegaly; this led to a diagnosis of autoimmune hemolytic anemia(AIHA). Steroid pulse therapy resulted in a dramatic halt in anemia progression. Given that AIHA is a paraneoplastic syndrome with suspected resistance to endocrine therapy, chemotherapy with paclitaxel was initiated. AIHA recurrence was not observed after this intervention. In cases of breast cancer with bone marrow metastasis and acute anemia, especially in patients with an autoimmune history, a differential diagnosis beyond marrow suppression from metastasis should be carefully considered.